1. Field of the Invention
The present invention relates to a cap member for an electrical double layer capacitor container.
2. Description of the Related Art
In recent years, electrical double layer capacitors of high capacity and high output have received attention as car-mounted electric power sources for driving cars.
There is known electrical double layer capacitors in which electrode elements are impregnated with an electrolytic solution and housed into a bottom-closed tubular container. The electrode elements have a positive electrode and a negative electrode oppositely placed on opposite sides of separators, wherein the positive electrode and the negative electrode are of solid electrodes including activated carbon and the like as a main ingredient and formed on the surfaces of current-collecting members of metal foil and the like.
In the above electric double layer capacitor, a highly wetting organic electrolytic solution is used in order to heighten electrode density when the above active carbon is impregnated with the above electrolytic solution. As such an organic electrolytic solution, a solution wherein a quaternary ammonium salt is dissolved in an organic solvent such as polycarbonate is used, for example.
Furthermore, in the electrical double layer capacitors, there is known a capacitor having such a configuration that the opening of the container is sealed by a cap member having a pair of electrode terminals connected to the respective electrodes. For example, Japanese Patent Application Laid-open No. 2000-21684 discloses a cap member for an electrical double layer capacitor comprising an insulating seal member formed by insert molding of a synthetic resin in between a metallic member provided with a through hole in the inner peripheral side and a pair of electrode terminals passing into the through hole. The cap member described in the application is ultra-sonic welded to the opening of a bottom-closed tubular container, thereby shielding and capping the opening.
However, the cap member is shrunk during solidification by cooling of a synthetic resin insert-molded. Therefore, this method has a disadvantage of a reduction in adhesion between the insulating seal member formed and the metallic member or the electrode terminal surface. The reduced adhesion results in a fear that when the inside of the electrical double layer capacitor becomes high pressured by the evolution of gas and the like, the organic electrolytic solution having high wettability may leak outside from a gap between the insulating seal member and the metallic member or the electrode terminal.
The present invention has an object to resolve such disadvantages and to provide a cap member for an electrical double layer capacitor permitting securely preventing of electrolytic solution therein from leaking to the outside even when the electrolytic solution is of high wettability.
In order to achieve this object, an aspect of the present invention is directed to a cap member for an electrical double layer capacitor which shields and caps an opening of a bottom-closed tubular container housing electrode elements of a positive electrode and a negative electrode impregnated with an electrolytic solution and oppositely placed via a separator and which has a pair of electrode terminals connected to each of the electrodes, said cap member comprising a first electrode terminal which is in the form of a hollow tube and arranged in the outer peripheral side of the opening, a second electrode terminal which is arranged via a predetermined space in the inner peripheral side of the first electrode terminal, and an insulating seal member consisting of a resin-molded article including glass fibers of small pieces inserted and formed between both the electrode terminals, wherein the first electrode terminal has a rib projecting downward from its bottom surface and extending in the axial direction of the container and chemically bonds to an organic compound layer formed on the surface of the first terminal, the second electrode terminal has a rib projecting upwardly from its bottom surface and extending in the axial direction of the container and chemically bonds to an organic compound layer formed on the surface of the second terminal, the bottom surface of the rib of the second electrode terminal is positioned above the bottom surface of the rib of the first electrode terminal, and the resin-molded article contains therein the ribs formed on both the electrode terminals and chemically bonds to the organic compound layers formed on the surfaces of both the electrode terminals.
In the cap member according to the present invention, there is a fear of a reduction in adhesion between the insulating seal member and both the electrode terminals because a resin injected in the molten state shrinks during solidification by cooling thereof.
Here, the shrinking force of the resin-molded article forming the insulating seal member largely acts in the radius direction of the first electrode terminal in the form of a hollow tube, that is, in the direction orthogonal to the axial direction of the container. For this reason, in the cap member according to the present invention, the electrode terminals each are provided with the ribs projecting downward from the respective bottom surfaces and extending in the axial direction of the container, and the resin-molded article is formed to contain therein the ribs formed on both the electrode terminals. As a result, according to the cap member of the present invention, the rib works against the shrinking force of the resin-molded article, thereby permitting the prevention of a reduction in adhesion between the insulating seal member and both the electrode terminals.
Furthermore, in the cap member according to the present invention, both the electrode terminals chemically bond to the organic compound layers formed on their respective surfaces, and the resin-molded article chemically bonds to the organic compound layer. As a result, in the cap member according to the present invention, excellent adhesion can be provided between the insulating seal member and both the electrode terminals through the medium of the organic compound layers to which each of them chemically bonds as described above.
As the above organic compound layer, the layer comprising a silane coupling agent or a triazinethiol derivative may be mentioned.
On the other hand, in order to be chemically bonded to the above organic compound layer, the above resin-molded article is preferably made of one resin selected from the group consisting of a nylon, an acrylonitrile-butadiene-styrene copolymer resin, polybutylene terephthalate, polyphenylene sulfide, polyphenylene oxide, an epoxy resin, and a phenol resin.
According to the cap member of the present invention, it is possible to prevent a reduction in adhesion between the insulating seal element and both the electrode terminals to hold excellent adhesion between them. Therefore, in the case of using an organic electrolytic solution of high wettability, it is possible to securely prevent the organic electrolytic solution from leaking.
Furthermore, in the cap member according to the present invention, it is characterized that the resin-molded article is formed by insert molding comprising the steps of placing a mold having an inner surface shape coincident with the outside shape of the insulating seal member and the second electrode terminal in the inner peripheral side of the first electrode terminal, injecting a molten resin from a gate provided on the surface facing the second electrode terminal in the inner peripheral side of the mold into the mold, entering the injected resin along the surface of the inner peripheral side of the mold into the side of the second electrode terminal, guiding the resin hitting the bottom surface of the second electrode terminal to the rib of the second electrode terminal for the resin to backwardly flow in the direction of the gate, guiding the resin hitting the bottom surface of the gate side of the mold to the rib of the first electrode terminal for the resin to flow between both the electrode terminals, and allowing a part of the resin hitting the bottom surface of the gate side of the mold to flow in the outer peripheral side of the rib of the first electrode terminal.
In the insert molding, the cap member according to the present invention has the bottom surface of the rib of the second electrode terminal positioned upwardly of the bottom surface of the rib of the first electrode terminal. Therefore, the molten resin is easy to flow into behind the rib of the second electrode terminal when viewed from the flowing-in direction of the resin, that is, in the side of the first electrode terminal, thereby permitting easy molding of the insulating seal member.
Further, in the cap member according to the present invention, during insert molding of the insulating seal member as described above, the resin injected in the molten state is guided by the rib to snake upward and downward in the axial direction of the container as described above. As a result, in the resin-molded article configuring the insulating seal member, the contained glass fibers of small pieces is oriented in the direction almost parallel to the axial direction of the container. Therefore, in the cap member according to the present invention, the glass fibers of small pieces oriented as described above cause a force acting against the shrinking force of the resin-molded article, thereby permitting prevention of a reduction in adhesion between the insulating seal member and both the electrode terminals.
Although the cap member according to the present invention is fixed to the outer peripheral side of the opening of the bottom-closed tubular container via the first electrode terminal, thus capping the opening, at this time, the electrode terminal is welded to the opening by laser welding and the like. Therefore, the cap member of the present invention is characterized in that when the first electrode terminal is welded to the opening of the bottom-closed tubular container, the resin-molded article is formed so that a space is left between its end portion facing the side wall of the bottom-closed tubular container, and the welded portion of the electrode terminal and the opening.
As described above, the cap member according to the present invention has a space between the end portion of the resin-molded article and the side wall of the bottom-closed tubular container, and therefore it is possible to prevent the heat generated by the laser welding and the like from degrading the resin-molded article configuring the insulating seal member. Therefore, in the cap member according to the present invention, the insulating seal member and both the electrode terminals can hold excellent adhesion to each other.